Friday, October 12, 2007

Al Gore's An Inconvenient Truth: unscientific?

It has been a week of contrasts for Al Gore. No doubt he has spent much of it wondering if he should prepare champagne for breakfast on Friday, with rumors running wild over whether or not he should and would win the 2007 Nobel Peace Prize. Just this morning, the announcement was made: the prize is his - or at least half of it. The other half goes to the Intergovernmental Panel on Climate Change.

Meanwhile, over in the UK, a judge criticised Al Gore's Oscar-winning movie An Inconvenient Truth for a series of inaccuracies. The ruling concludes a case brought to the UK High Court by Stuart Dimmock, a parent of two who was concerned to find that the UK Department for Education and Skills had distributed a copy of Gore's film to every state secondary school in the UK.

He argued that the film was political material, had no place in the classroom, and that its distribution to schools should be made illegal. Moreover, his legal team pointed out a list of alleged scientifically inaccuracies in the film.

The judge, Justice Burton, declined to make it illegal. In his ruling, however, he says Gore committed nine counts of scientific inaccuracy.

But was the judge right?

Sea level rise of up to 7 metres will be caused by melting of either west Antarctica or Greenland in the near future.

Burton: This is distinctly alarmist... It is common ground that if indeed Greenland melted, it would release this amount of water, but only after, and over, millennia, so that the Armageddon scenario he predicts, insofar as it suggests that sea level rises of 7 metres might occur in the immediate future, is not in line with the scientific consensus.

Gore does not explicitly say that Greenland’s ice will disappear in the immediate future, merely that coastal areas will be dramatically flooded very soon. That point aside, there is, as Burton says, some debate over how quickly the ice caps – and Greenland in particular – could melt.

Burton: According to the IPCC, it is very unlikely that the Ocean Conveyor (known technically as the Meridional Overturning Circulation or thermohaline circulation) will shut down in the future.

Gore suggests that this density-driven ocean circulation system could collapse in the North Atlantic if it were to receive a large influx of cold water. The 2007 assessment of the IPCC states that it is very unlikely that the ocean conveyor belt will shut down, but very likely that it will slow down by 2100 (p. 16 of WGI summary for policymakers).

Gore implies that this could happen if the Greenland ice sheet melts. In 2006, a team of researchers led by Kirsten Zickfeld of the University of Victoria in Canada carried out a poll of 12 scientists on this question. Eight said they believed there was a 40% chance the conveyor belt would collapse if global average temperature rose by more than 4°C above pre-industrial levels. How much temperatures rise depends entirely on how society evolves and on our future energy supply.

There is a direct relationship between historic rise in CO2 in the atmosphere and in temperature

Burton: Mr Gore shows two graphs relating to a period of 650,000 years, one showing rise in CO2 and one showing rise in temperature, and asserts (by ridiculing the opposite view) that they show an exact fit. Although there is general scientific agreement that there is a connection, the two graphs do not establish what Mr Gore asserts.

Burton: Mr Gore asserts that the disappearance of snow on Mt Kilimanjaro is expressly attributable to global warming. However… the scientific consensus is that it cannot be established that the recession of snows on Mt Kilimanjaro is mainly attributable to human-induced climate change.

Only 21% of the 1912 ice cover on Kilimanjaro was still around in 2003. Whether or not the melting of Kilimanjaro's snow and ice cap is a symptom of global warming has long been a subject of debate. In 2006, a team of scientists apparently put the controversy to bed with a 2006 study led by Nicolas Cullen of the Tropical Glaciology Group at the University of Innsbruck. Using recent high-resolution satellite images, Cullen's team came to the conclusion that "rather than changes in 20th century climate being responsible for their demise, glaciers on Kilimanjaro appear to be remnants of a past climate that was once able to sustain them".Read more about the study here.

Burton: The drying up of Lake Chad is used as a prime example of a catastrophic result of global warming. However, it is apparently considered to be far more likely to result from other factors, such as population increase and over-grazing, and regional climate variability.

According to NASA: "Using model and climate data, Coe and Foley calculate that a 30% decrease took place in the lake between 1966 and 1975. Irrigation only accounted for 5% of that decrease, with drier conditions accounting for the remainder. They noticed that irrigation demands increased four-fold between 1983 and 1994, accounting for 50% of the additional decrease in the size of the lake." Read more here.

The impact of Hurricane Katrina was due to global warmingBurton: Hurricane Katrina and the consequent devastation in New Orleans is ascribed to global warming. It is common ground that there is insufficient evidence to show that.

There is still considerable debate over the link between the strength of hurricanes and climate change, yet given that hurricanes collect their power from the temperature of surface water, there is a plausible physical link. One paper published recently comes down more strongly in favour of a link than any other previous study. I recently discussed this finding with a hurricane specialist at the UK Met Office and according to him the debate is still not resolved.

Certainly, when Gore’s film came out there was no definitive evidence for a link. Also, very few scientists would try to link a single weather event to climate change. Studies can say whether the probability of an event happening increases with global warming, though, so far as I know, none has yet been carried out on Katrina.

Burton: Mr Gore says: "A new scientific study shows that for the first time they are finding polar bears that have actually drowned swimming long distances up to 60 miles to find the ice. They did not find that before." The only scientific study that either side before me can find is one which indicates that four polar bears have recently been found drowned because of a storm. That is not to say that there may not in the future be drowning-related deaths of polar bears if the trend continues.

In September 2004, four polar bears were found dead, floating in Arctic waters - an unprecedented observation. The authors of the report in Polar Biology speculate that they may have died of exhaustion and this might have been a result of shrinking sea ice. They propose that polar bears may increasingly meet an untimely death for this reason.

Charles Monnet, first author on the paper, told New Scientist that "he doubts this was simply the result of exhaustion from having to swim further from ice to shore. More likely, weather conditions are becoming more severe in the growing expanses of open water, making swimming more difficult." Read more about the fate of polar bears and other animals here.

Coral reef bleaching events are due to global warming

Burton: Mr Gore says: "Coral reefs all over the world because of global warming and other factors are bleaching." [According to] the IPCC report, if the temperature were to rise by 1 °C to 3 °C, there would be increased coral bleaching and widespread coral mortality, unless corals could adopt or acclimatise, but that separating the impacts of climate change-related stresses from other stresses, such as over-fishing and polluting, is difficult.

I will let you judge for yourselves whether Gore's movie deserves the label "unscientific".

For my part, I would say that strictly speaking, Gore oversimplified certain points, made a few factual errors and, at times, chose the wrong poster child (Mount Kilimanjaro should have been replaced by any number of Alaskan or Andean glaciers, for instance). It's unfortunate, but it remains the most comprehensive popular documentary on climate change science I have seen.